System and method for illumination attenuation

ABSTRACT

Generally speaking, the output brightness of an illuminator is varied by chopping an output light beam such that the beam is alternately interrupted and unhindered. An interrupter can be rapidly moved into and out of the transmission path of a light beam. The brightness of the light beam received at a site will be attenuated based on the amount of time per cycle the light beam remains obstructed versus unhindered.

This application is a divisional of U.S. application Ser. No. 11/561,718filed on Nov. 20, 2006, now U.S. Pat. No. 7,760,411.

TECHNICAL FIELD OF THE INVENTION

Embodiments of the present invention relate to systems and methods forattenuating the brightness of a light beam. More particularly,embodiments of the present invention relate to systems and methods fortime domain attenuators.

BACKGROUND OF THE INVENTION

Surgical instrumentation often uses fiber optics to direct light from alight source, such as a laser, LED or other light source, to a surgicalhand piece. The tip of the surgical hand piece is then used to directthe light to the eye. In some cases, it is desirable to attenuate thebrightness of the light received at the eye. Currently, position domainattenuators that proportionally interrupt part, or all, of a light beamare used. In these systems, a non-optically transmissive element ispositioned to prevent a part of the light beam from reaching the targetfiber, resulting in some attenuation. Position domain attenuatorsinclude rotating louvers, variable slot width obstructions, varyingaperture size obstructions and varying neutral density filters. Byobstructing just a portion of the light beam, the quality of theilluminated spot projected from the end of the fiber can be affected.For example, the projected spot on the eye may have a bright center fromthe light that is not obstructed as well as shadow and color rings fromthe light that was obstructed. Indeed, the center of the spot mayexhibit no attenuation, while the edges of the spot are highlyattenuated. This result can be undesirable as it provides an unevenenergy distribution to the eye.

Another current attenuation approach includes adjusting the voltage orcurrent of the light source, thereby changing the intensity of theproduced light. While this approach can evenly attenuate the brightnessof the light spot received at the eye, it suffers the shortcoming thatthe color temperature of the light is typically changed.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide systems and methods forattenuating the brightness of a light beam. Broadly speaking, aninterrupter is moved completely into and fully out of the path of thelight beam. This chopping of the light beam attenuates the beam. If themovement of the interrupter is quick enough and the repetition rate ofthe interrupter cycle high enough, the interruption of the light beam isnot perceived by the human eye and the light beam simply appearsattenuated.

Embodiments of the present invention include a light attenuation systemcomprising a light source to project a light beam, an interrupteroperable to move into and out of a path of the light beam, a motor(actuator) coupled to the interrupter to move the interrupter from aposition in which the light beam is unhindered by the interrupter to aposition in which the light beam is incident on the interrupter, and acontroller operable to control the motor and cause the motor to move theinterrupter with a repetition rate so that the light beam is unhinderedfor a first portion of a cycle and the light beam is incident on theinterrupter for a second portion of the cycle. When the light beam isincident on the interrupter, it can be fully incident on theinterrupter. Attenuation can thus be achieved without affecting thecolor temperature of the light.

Another embodiment of the present invention can include a set ofcomputer instructions comprising instructions executable to receive oneor more attenuation control parameters. The attenuation controlparameters can include any variables that can be user specified. Inaccordance with the implementation, these can include duty cycle, cycletime, repetition rate, attenuation level or other parameters. Based onthe received control parameters and/or predefined control parameters,the instructions are executable to determine a control scheme. Forexample, the controller can determine the amount of time that a lightbeam should be fully interrupted and unhindered. Accordingly, thecontrol scheme is configured to cause an interrupter to move into andout of a path of a light beam for a plurality of cycles with arepetition rate to attenuate the light beam's brightness.

Yet another embodiment of the present invention includes a method forattenuating light comprising projecting a light beam along a path andmoving an interrupter into and out of the path of the light beam for aplurality of cycles with a repetition rate to attenuate the light beam'sbrightness without affecting the color temperature of the light beam.The light beam is unhindered by the interrupter for a first portion ofeach cycle and is incident (e.g., fully incident) on the interrupter forthe second portion of the cycle.

Another embodiment of the present invention includes a method forattenuating light comprising projecting a light beam along a path andmoving an interrupter into and out of the path of the light beam for aplurality of cycles with a repetition rate to create attenuated lightthat appears attenuated and continuous to the human eye. According toone embodiment light beam is unhindered by the interrupter for a firstportion of each cycle and is incident (e.g., fully incident) on theinterrupter for the second portion of the cycle.

Embodiments of the present invention provide an advantage over the priorart by attenuating the brightness of a light beam while minimizingdeleterious effects such as shadow and color rings caused by positiondomain attenuators.

Embodiments of the present invention provide another advantage byallowing for attenuation of a light beam without changing the colortemperature of the light, as occurs with attenuation schemes in whichthe intensity of the light source is varied by reducing the powerdelivered to the light source.

BRIEF DESCRIPTION OF THE FIGURES

A more complete understanding of the present invention and theadvantages thereof may be acquired by referring to the followingdescription, taken in conjunction with the accompanying drawings inwhich like reference numbers indicate like features and wherein:

FIGS. 1A and 1B are diagrammatic representations of one embodiment of asystem for attenuating a light beam in a surgical system utilizing fiberoptics.

FIGS. 2A-2B are diagrammatic representations of another embodiment of asystem for attenuating a light beam;

FIGS. 3A-3B are diagrammatic representations of yet another embodimentof a system for attenuating a light beam; and

FIG. 4 illustrates example duty cycles for various levels ofattenuation.

DETAILED DESCRIPTION

Preferred embodiments of the invention are illustrated in the FIGURES,like numerals being used to refer to like and corresponding parts of thevarious drawings.

Embodiments of the present invention provide systems and methods forattenuating light in a manner that reduces or eliminates the shadow andcolor ring effects of position domain attenuators without affecting thecolor temperature of the light. In other words, embodiments provide foreven attenuation of the light beam without affecting the quality of theintensity distribution or color of the light.

Generally speaking, the output brightness of an illuminator is varied byalternately chopping the light beam such that the beam is both fullyinterrupted and fully unhindered. An interrupter can be rapidly movedinto and out of the transmission path of a light beam. The brightness ofthe light beam received at a site will be attenuated based on the amountof time per cycle the light beam remains obstructed and unhinderedbecause less light will be received at the site per unit of time.

For purposes of explanation, the term “cycle time” of the interrupter isthe sum of the unhindered and interrupted time for a cycle, the“repetition rate” is the number of cycles in a given time period, andthe “duty cycle” is the ratio of unhindered time to the cycle time. Therepetition rate is essentially the frequency of the interrupter, butpreferably with a square profile rather than a sinusoidal profile. Theduty cycle can range from 0% (no light passes) to 100% (no attenuation).

Preferably, the interrupter is moved into and out of the path of thelight beam at a repetition rate such that the interruption of the beamis not perceived as flashing light by the human eye. To achieve this,the repetition rate should be greater than 30 cycles and preferablygreater than 60 cycles per second. Although usable, certain repetitionrates may not be preferred. For example, background lights in thesurgical theater can flicker at certain frequencies (e.g., 60 cycles persecond in the United States and 50 cycles per second in other areas).Such lights may produce interference with an attenuator running at 60 or50 cycles a second, depending on location. The brightness of a lightbeam compared to its un-attenuated state is approximately proportionalto the duty cycle of the interrupter. Using the example of a repetitionrate of 75 cycles per second, the cycle time is approximately 13.3milliseconds. If the duty cycle is 40%, meaning that the light isunhindered for 5.32 milliseconds of the cycle, the attenuated light beamwill appear to be approximately 40% as bright as the un-attenuated lightbeam. Brightness adjustment can be achieved by changing the duty cycleof the interrupter and by changing the repetition rate as necessary tomaintain the experience of non-flashing (i.e., continuous) light.According to various embodiments, the interrupter can be linearly placedinto and removed from the light beam or rotated into and out of thelight beam.

FIGS. 1A and 1B are diagrammatic representations of one embodiment of asystem 100 for attenuating a light beam in a surgical system utilizingfiber optics. In system 100, a light source projects a light beam 104 toan optical fiber 106. Light source 102 can comprise light sources suchas a xenon light source, a laser, an LED or other light source used toilluminate or ablate tissue. Optical fiber 106 can be a plastic, glassor other material fiber that guides light from light beam 104 to asurgical handset or otherwise guides light to a surgical site. Linearactuator (linear motor, solenoid, pneumatic cylinder, hydrauliccylinder, etc.) 108 moves an interrupter 110 into and out of the path oflight beam 104 between the light source and optical fiber 106.Interrupter 110 moves from a position in which light beam 104 isunhindered by interrupter 110 (shown in FIG. 1A) to a position in whichlight beam 104 is fully incident on interrupter 110 (shown in FIG. 1 B).It should be noted that system 100 can include other optical componentslocated between optical fiber 106 and light source 102. Additionally,the path of light beam 104 may not be straight.

A controller 112 can control the motion of linear actuator 110.Controller 112 can include any suitable controller that can receive datafrom various components of system 100. Controller 112 can include aprocessor 114 (such as an ASIC, CPU, DSP or other processor) andcomputer instructions 116 executable by processor 114 (e.g., software orother instructions stored on a computer readable medium). Instructions116 can be stored on a computer readable memory 118 (e.g., hard drive,Flash memory, optical memory, RAM, ROM, processor memory or othercomputer readable medium known in the art). Controller 112 can includeany number of additional computer components. For example, controller112 can include an analog to digital converter 120 to convert signalsfrom linear actuator 108 to digital signals, and a digital to analogconverter 122 to convert signals from processor 114 to analog controlsignals. While shown as communicating electrical analog signals to alinear actuator 108, controller 112 can send electrical digital oranalog, or pneumatic, control signals to actuator 108 or to othercontrollers to cause actuator 108 to operate according to a particularcontrol scheme. Additionally, while controller 112 is shown as a singleblock in FIG. 1 for the sake of simplicity, the control functionality ofsystem 100 can be distributed among multiple processors.

In operation, linear actuator 108 is controlled to move interrupter 110into and out of light beam 104. In the embodiment of FIG. 1 in which alinear motor is used, interrupter 110 reciprocates from a position inwhich light beam 104 is unhindered (e.g., as shown in FIG. 1A) and aposition in which light beam is fully incident on interrupter 110 (e.g.,as shown in FIG. 1B). In other words, the stroke of linear actuator 108is sufficient to linearly position the interrupter fully into the lightbeam. Preferably, interrupter 110 is made of a non-transmissive materialto fully block light beam 104 when light beam 104 is fully incident oninterrupter 110. As one example, interrupter 110 can be formed ofaluminum.

According to various embodiments, controller 112 can receive attenuationcontrol parameters that affect the control scheme according to whichcontroller 112 controls actuator 108. These parameters can include, forexample, duty cycle and repetition rate or other parameters. In otherembodiments, one or more of the attenuation control parameters can bepredefined at controller 112.

Controller 112 can, for example, control linear actuator 108 to have aparticular repetition rate and duty cycle. The duty cycle can range from0 to 100% of the cycle time. Preferably, the repetition rate is selectedso that if the duty cycle is greater than 0% and less than 100% of thecycle time, the human eye will not perceive flickering of the light (at0% duty cycle, the interrupter is continuously in the path of light beam104 and, at 100% duty cycle, the interrupter does not interrupt thelight beam 104). Generally, repetition rates of greater than 60 cyclesper second will not be visible to the human eye so that the resultinglight appears continuous and attenuated.

Actuator 108 can be selected to have sufficient energy to moveinterrupter 110 between states in which light beam 104 is unhindered toa state where light beam 104 is fully incident on interrupter 110 in asshort a time as possible to minimize the transition period in whichlight beam 104 is only partially incident on interrupter 110.Furthermore, controller 112 can account for the fact that actuator 108is moving a mass that must accelerate and decelerate to reciprocate.Consequently, interrupter 110 may be moving in the time in which lightbeam 104 is fully unhindered and the time in which light beam 104 isfully incident on interrupter 110. For example, if the cycle time is13.3 milliseconds and the time that light beam 104 is fully incident oninterrupter 110 is 8 milliseconds, interrupter 110 can be moving duringthe 8 milliseconds it is blocking light beam 104.

In the above example, a linear actuator is used to selectively interruptlight beam 104. FIGS. 2A and 2B are diagrammatic representations ofanother embodiment of the present invention in which a rotary actuator124 rotates interrupter 126 into and out of the path of beam 104.Actuator 124 can be a rotary motor, a rotary action hydraulic orpneumatic device to impart rotary motion or other rotary actuator.According to one embodiment, rotary actuator 124 can rotate back andforth to move interrupter 126 into and out of the path of light beam104. According to one embodiment, rotary actuator 124 alternatelyrotates 90 degrees. Again, the repetition rate can be selected so thatinterruption of the light beam is not perceived by a human eye to whichlight is directed by optical fiber 106.

FIGS. 3A and 3B are diagrammatic representations of yet anotherembodiment that utilizes a rotary actuator 128 to move interrupter 130into and out of the path of light beam 104. In the example of FIGS. 3Aand 3B, interrupter 130 is coupled to actuator 128 by an arm 132. Asactuator 128 moves arm 132, interrupter 130 swings into and out of thepath of light beam 104. For example, rotary actuator 128 can alternatelyrotate a set number of degrees, say 30 degrees, to swing interrupter 130into the path of light beam 104 to fully block light beam 104 and out ofthe path of light beam 104 to leave light beam 104 unhindered byinterrupter 130. According to other embodiments, interrupter 130 canswing through an arc such that for one cycle interrupter 130 is on oneside of the beam path when light beam 104 is unhindered and for the nextcycle is on the other side of the beam path when light beam 104 isunhindered. Controller 112 can control actuator 128 such that aparticular repetition rate and duty cycle are achieved.

FIG. 4 is a set of graphs representing one embodiment of cycle statesfor various levels of attenuation of light beam 104. In the example ofFIG. 4, the cycle time is 16 milliseconds, corresponding to a repetitionrate of 62.5 cycles per second. Line 140 represents a 25% duty cycle,line 142 represents a 50% duty cycle and line 144 represents a 75% dutycycle. As can be seen from line 140, the interrupter 130 is in aposition in which light beam 104 is fully unhindered for approximately 4milliseconds and fully blocked for 12 milliseconds, resulting in 75%attenuation of light beam 104 (i.e., light beam 104 will only appear tobe 25% as bright downstream of the interrupter 130 as it appearsupstream of interruptor 130). During each state (e.g., the fullyblocking and the fully non-blocking state) the interrupter 130 can stillbe moving, so the states of the interrupter 130 with respect to lightbeam 104 may, but do not necessarily, correspond to the actuator 128states. In other words, a graph of the actuator 128 state may bedifferent than the graph of the interrupter 130 state relative to lightbeam 104.

The transitions (e.g., transition 146 and transition 148) between afully blocking and fully non-blocking state shown in FIG. 4 are shown ascorresponding to a square wave. That is, they are shown as instantaneoustransitions. In practice, there is some small transition zone in whichlight beam 104 is only partially blocked. If that transition zone is toolong, some of the negative effects of position domain attenuators, suchas shadow rings, may be seen briefly. Therefore, it is preferable tomake the transition as close to ideal as possible to minimize thetransition time.

Embodiments of the present invention thus provide a light attenuationsystem comprising a light source to project a light beam, an interrupteroperable to be positioned into and out of a path of the light beam, anactuator coupled to the interrupter and operable to move the interrupterfrom a position in which the light beam is unhindered by the interrupterto a position in which the light beam is fully incident on theinterrupter, and a controller operable to control the actuator and causethe actuator to move the interrupter with a repetition rate so that thelight beam is unhindered for a first portion of a cycle and the lightbeam is fully incident on the interrupter for a second portion of thecycle to attenuate the light beam's brightness. Attenuation can thus beachieved without affecting the color temperature of the light.

Another embodiment of the present invention can include a set ofcomputer instructions comprising instructions executable to receive oneor more attenuation control parameters. The attenuation controlparameters can include any variables that can be user specified.According to the particular implementation, these can include dutycycle, cycle time, repetition rate, attenuation level or otherparameters. Based on the received control parameters and/or predefinedcontrol parameters, the instructions are executable to determine acontrol scheme. For example, if the system has a preprogrammedrepetition rate, the instructions can be executable to receive a dutycycle or other parameters. Based on the received parameters and thepredefined repetition rate, the amount of time that a light beam isfully interrupted versus unhindered can be determined. Accordingly, thecontrol scheme is configured to cause an interrupter to move into andout of a path of a light beam for a plurality of cycles with arepetition rate to attenuate the light beam's brightness. In general,the light beam is unhindered by the interrupter for a first portion ofeach cycle and is fully incident on the interrupter for the secondportion of the cycle.

The instructions can be further executable to generate one or morecontrol signals to cause an actuator to move the interrupter into andout of the path of the light beam according to the control scheme. Thecontrol signals can be sent to the actuator, another control or othercomponent that can cause the actuator to move according to the controlscheme.

While the present invention has been described with reference toparticular embodiments, it should be understood that the embodiments areillustrative and that the scope of the invention is not limited to theseembodiments. Many variations, modifications, additions and improvementsto the embodiments described above are possible. It is contemplated thatthese variations, modifications, additions and improvements fall withinthe scope of the invention as detailed in the following claims.

1. A computer program product comprising a non-transitory computerreadable medium storing a set of computer instructions, the set ofcomputer instructions comprising instructions executable by a processorto: receive one or more attenuation control parameters; determine acontrol scheme to cause an interrupter to move into and out of a path ofa light beam for a plurality of cycles with a repetition rate toattenuate the light beam's brightness, wherein the light beam isunhindered by the interrupter for a first portion of each cycle and isfully incident on the interrupter for the second portion of the cycle;and generate one or more control signals to cause an actuator to movethe interrupter into and out of the path of the light beam according tothe control scheme.
 2. The computer program product of claim 1, whereinthe repetition rate is selected so that light from the light beamattenuated by the interrupter appears attenuated and continuous to ahuman eye.
 3. The computer program product of claim 1, wherein therepetition rate is at least 30 cycles per second.
 4. The computerprogram product of claim 1, wherein the repetition rate is at least 60cycles per second.